Four component compact zoom lens

ABSTRACT

A compact zoom lens comprising four components each movable axially to vary the focal length through a range of at least 2.5:1. There is a front negative, a positive component, a positive cemented doublet component and a rear negative component comprising three elements. A diaphragm is mounted with the first-mentioned positive component.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to compact zoom lenses including four lens groupsall of which are axially movable.

2. Summary of the Invention

It is an object of the present invention to provide an objective zoomlens for a viewfinder camera, which is sufficiently compact that thefront end of the zoom lens does not intrude into the field of view ofthe viewfinder when the viewfinder is positioned desirably close to thetaking lens for avoiding viewfinder parallax. Obviously, both diameterof the front end of the zoom lens and the distance of the front end ofthe zoom lens from the film plane are factors in this problem. The lensmay also be light in weight and easily stored.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 schematically represents a first embodiment of the presentinvention;

FIGS. 2 and 3 are tables of constructional data for the firstembodiment, illustrated in FIG. 1;

FIG. 4 schematically represents a second embodiment of the presentinvention;

FIGS. 5 and 6 are tables of constructional data for the secondembodiment, illustrated in FIG. 4;

FIG. 7 schematically represents a third embodiment of the presentinvention; and

FIGS. 8 and 9 are tables of constructional data for the thirdembodiment, illustrated in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A first embodiment of the present invention, represented in FIG. 1, is azoom lens 21 intended to be the taking objective lens of a viewfindercamera. The lens 21 has an image plane 23 in which the film is disposedin the camera. The lens has an object plane 25. In the ensuingdescription, the front of the lens or of a component or element isnearer or towards the object plane 25.

The lens 21 includes four components, all of which are axially movable.There are: a front, first component 27; a second component 29; a thirdcomponent 31 and a fourth, rear component 33.

Front component 27 is a negative menicus lens element A having front andrear surfaces R₁ and R₂ and a thickness t₁. The values of the radii ofthe surfaces R₁, R₂ and the value of t₁ ae given in the table in FIG. 2.The front component 27 is utilized to adjust the image to focus at theimage plane 23. The object plane 25 is spaced by a variable distance S₁from the element A.

Spaced from front component 27 by a variable air gap is the secondcomponent 29, which is positive and includes a diaphragm DM and a doubleconvex lens element B having a front surface R₃, which is aspheric, anda rear surface R₄. The thickness t₃ of the lens element B is given inthe table in FIG. 2.

The aspheric surface R₃ conforms to the formula: ##EQU1## whereinC=0.02557865

K=12.0445

D=-0.37847×10⁻⁴

E=-0.26615×10⁻⁶

F=0.26087×10⁻⁸

G=-0.33251×10⁻¹⁰

X is the longitudinal coordinate of a point on the surface which is adistance Y from the X axis.

The position of the diaphragm DM is determined by the variable space S₂from the element A and by fixed distance FS from element B. Thediaphragm DM has a clear aperture of 17.20 mm, and is movable with thelens element B.

Spaced from the second component 29 by a variable air gap S₃ is thethird component 31 which is a positive cemented doublet including ameniscus lens element C and a double convex lens element D. The lenselement C has a front surface R₅, a rear surface R₆ and a thickness t₄.The double convex lens element D has front and rear surfaces R₆ and R₇,respectively, and a thickness t₅.

Spaced from the third component 31 by a variable air gap S₄ is thefourth component 33 which is a two units, both units being negative,three element component and is herein termed a negative negativecomponent. The fourth, negative negative component includes a frontmeniscus lens element E having front and rear surfaces R₈ and R₉,respectively, and thickness t₇, a middle meniscus lens element F havingfront and rear surfaces R₁₀ and R₁₁ and thickness t₉, and a doubleconcave lens element G having front and rear surfaces R₁₂ and R₁₃, andthickness t₁₁. The lens elements E and F are spaced by a fixed distanceFS₂ at the vertices of their surfaces R₉ and R₁₀. The lens elements Fand G are spaced by a fixed distance FS₃ at the vertices of theirsurfaces R₁₁ and R₁₂.

As each of the four moving components increases (or decreases) itsdistance from its adjacent component, the change in focal length withrespect to increasing (or decreasing) incremental space is of the samesign for each component. Thus, every component has a constructivecontribution to the decrease (or increase) of the focal length. Thiscontributes to the large zoom ratio and short front vertex to imageplane distance exhibited.

The variation in space S₄ between components 31 and 33 contributes tothe focal length change four or five times more than equal increments ofvariation in space S₃ and two to three times more than equal incrementsof variation in space S₂. The actual magnitude of the ratios depends onwhether the lens is in wide angle or telephoto configuration.

Besides changing focal length, the increments of change of spaces S₂, S₃and S₄ also partially compensate for aberrations, especially thespherical aberration in the telephoto configuration. The negativespherical aberration that results as spaces S₂ and S₄ are varied iscompensated for by the positive spherical aberration that results asspace S₃ is varied. This contributes to the stability of the aberrationover the large zoom ratio.

It has been found that with four movable components aberrations arecontrolled to acceptable levels and a relatively large back focus ismaintained.

In the third component 31, if the ratio VR_(CD) of the Abbe numbers ofthe elements C and D is computed so that VR_(CD) is greater than unity(i.e., of the two possible ratios a:b and b:a, that one is selectedwhich gives a value greater than unity) then 3>VR_(CD) >1.8. With suchparameters axial color is corrected.

In the fourth component 33 the choice of glasses is such that the ratioVR_(EF) of the Abbe numbers of the elements E and F is computed so thatVR_(EF) is greater than unity (i.e., of the two possible ratios a:b andb:a, that one is selected which gives a value greater than unity) then3>VR_(EF) >1.3. If these parameters are not observed axial and lateralcolor correction will not be achievable.

In order to control higher order distortion in the wide angle mode andbalance the distortion and lateral color over the full zoom range, thefollowing relationship exists:

    0.4>|N.sub.C -N.sub.D |>0.1

wherein

N_(C) is the refractive index of element C; and

N_(D) is the refractive index of element D.

The focal lengths of each of the four components, as well as the ratio Lof those lengths to the minimum effective focal length F_(s) are givenin the ensuing table:

    ______________________________________                                        Component    Focal Length F                                                                            L = F/F.sub.s                                        ______________________________________                                        27           -49.27 mm   -1.41                                                29           27.73 mm    0.79                                                 31           55.29 mm    1.58                                                 33           -25.12 mm   -0.72                                                ______________________________________                                    

The lens 21 is a positive-negative zoom lens in that the first threecomponents 27, 29 and 31 together have a positive net power, and therear component 33 has a negative power. The positive-negativearrangement tends to make the lens telephoto in the longer focal lengthmodes. The table in FIG. 3 gives the back focal length; lens length;length from front vertex of the front element to the image plane (i.e.,the sum of lens length and back focal length); and the telephoto ratio(i.e., length from front vertex of the front element to the image planedivided by the focal length), for each of four focal lengths includingthe two extreme focal lengths. As elsewhere in this specification, alllinear dimensions are in mm. It will be seen that at the longest focallength, the lens has a telephoto ratio of 0.93 which is an indication ofcompactness. In the wide angle mode, the lens has a length, 50.68 mm,which, together with the back focal length of 8.25 mm, renders the lenscomparable in its forward protrusion to a normal taking lens of a 35 mmcamera which typically extends 58 mm in front of the film plane. In thatthe camera for which the lens is intended is a camera with a separateviewfinder, it is important that the forward protrusion of the lens notbe such as to obscure a portion of the field of view of the viewfinder.

The ratio of the extreme focal lengths of this embodiment is104.56:35.06; i.e. 2.98:1 which would normally be termed a 3:1 zoomlens.

From FIG. 3 it will be seen that at a focal length of 35.06 mm, beingF_(s), the shortest focal length, the length from the vertex of thefront surface R₁ of the front element A to the film plane 23 is 58.93mm, and the telephoto ratio, i.e., the ratio of that length to the focallength, F_(s), is 1.68 which is less than 1.8. Also, at the long focallength, F_(L), of 104.56 mm, the length from the front surface R₁ of thefront element A to the film plane 23 is 97.15 mm, which is less than thefocal length F_(L).

The clear aperture of lens A is 15.91 mm which, together with theshortness of the distance between the vertex of the front surface R₁ ofthe front lens A and the film plane 23, ensures that a separateviewfinder can be placed close to the zoom lens without intruding on thefield of view of the viewfinder, thus minimizing viewfinder parallax.

FIG. 4 illustrates a second embodiment of the present invention which isgenerally similar in construction to the first embodiment describedabove. FIGS. 5 and 6 are tables giving the values for the variousparameters. In FIGS. 4 and 5, the four components are given the samereference numerals but with a prime (') suffix. Similarly, the lenselements are given the same reference letters but with a prime (')suffix. Likewise, the variable spacings are given the same referencesbut with a prime (') suffix.

In this second embodiment, the diaphragm DM' is placed behind theelement B' at a fixed distance FS₂₂ and a baffle BF is included in frontof element B' at a fixed distance FS₂₁. The variable spacing S₂ ' isbetween the element A' and the baffle BF. The variable spacing S₃ ' isbetween the diaphragm DM' and the component 31'.

Again, in this second embodiment, the third component 31' is a cementeddoublet. However, in this embodiment, in the fourth component 33'; whichagain is a triplet, the lens elements E' and F' are cemented.

In this second embodiment, the aspheric surface R₂₃ of the second lenselement B', has the formula: ##EQU2## wherein C=0.03467647

D=-0.42786×10⁻⁴

E=-0.11867×10⁻⁶

F=0.98374×10⁻⁸

G=-0.75315×10⁻¹⁰

and its vertex radius is 28.838 mm.

The focal lengths of each of the four components, as well as the ratio Lof those lengths to the minimum effective focal length, F_(s), are givenin the ensuing table:

    ______________________________________                                        Component    Focal Length F                                                                            L = F/F.sub.s                                        ______________________________________                                        27'          -54.75 mm   -1.56                                                29'          27.01 mm    0.77                                                 31'          45.32 mm    1.29                                                 33'          -19.38 mm   -0.55                                                ______________________________________                                    

The ratio of the extreme focal lengths of the second embodiment is104.79:35.02, i.e., 2.99:1.

From FIG. 6 it will be seen that at a focal length of 35.02 mm, beingF_(s), the shortest focal length, the length from the vertex of thefront surface R₂₁ of the front element A' to the film plane 23' is 57.56mm and the telephoto ratio, i.e., the ratio of that length, 57.56 mm, tothe focal length, F_(s), is 1.64 which is less than 1.8. Also, at thelong focal length, F_(L), of 104.79 mm, the length from the frontsurface R₂₁ of the first element A' to the film plane 23' is 93.01 mmwhich is less than the focal length F_(L).

The clear aperture of the lens A' is 21.70 mm which, together with theshortness of the distance between the vertex of the front surface R₂₁ ofthe front lens A' and the focal plane 23', ensures that a separateviewfinder can be placed close to the zoom lens without intruding on thefield of view of the viewfinder, thus minimizing viewfinder parallax.

FIG. 7 illustrates a third embodiment of the present invention and FIGS.8 and 9 are tables giving the values of various parameters. In FIGS. 7and 8, the components are given the same reference numerals as theircounterparts in the first embodiment described above and illustrated inFIG. 1, but with the addition of a double prime (") suffix. Similarly,the lens elements are given the same reference letter (with an exceptiondescribed below), but with the addition of a double prime (") suffix.Likewise, the variable spacings are given the same reference but with adouble prime suffix added.

Again, in this third embodiment, the third component 31" is a cementeddoublet and, as in the case of the second embodiment, the lens elementsE" and F" in the fourth component 33" are a cemented doublet.

In this third embodiment, the second component 29" is a doublet insteadof a singlet. In the first and second embodiments, the lens elements Band B' are both glass with one aspheric surface, namely R₃ on lenselement B, and R₂₃ on lens element B'. In order to avoid forming anaspheric surface on a glass element, the third embodiment places theaspheric surface R₄₃ on a plastic lens element B_(a) " and has a glasslens element B_(b) " with two spherical surfaces R₄₅ and R₄₆. Asphericsurfaces are relatively easily formed on plastics material elements.Plastic lenses are relatively susceptible to temperature changes. Whensubjected to a temperature change, their focal lengths change greaterthan is the case with glass. In order to avoid such disadvantageouseffect, the plastic lens element B_(a) " has no power. The glass elementB_(b) " has power but glass is markedly less susceptible to power changewith temperature change than is the case with plastics material.

In this third embodiment, the diaphragm DM" is placed at the rear of thesecond component 29" and there is no baffle in front of the secondcomponent. The variable spacing S₂ " is between the element A" and theelement B_(a) ". The fixed spacing FS₃₂ is between the element B_(b) "and the diaphragm DM". The variable spacing S₃ " is between thediaphragm DM" and the third component 31.

The aspheric surface R₄₃ again has the formula: ##EQU3## whereinC=0.0307541

D=-0.6111104×10⁻⁴

E=-0.2224872×10⁻⁶

F=0.7541840×10⁻⁹

G=-0.1842949×10⁻¹⁰

K=7.0508870

The focal lengths of each of the four components, as well as the ratio Rof those lengths to the minimum effective focal length, Fs, are given tothe ensuing table:

    ______________________________________                                        Component    Focal Length F                                                                            L + F/F.sub.s                                        ______________________________________                                        27"          -59.28 mm   -1.69                                                29"          27.81 mm    0.79                                                 31"          47.86 mm    1.37                                                 33"          -19.87 mm   -0.57                                                ______________________________________                                    

The ratio of the extreme focal lengths of the third embodiment is104.88:35.01, i.e., 3.00:1

From FIG. 9 it will be seen that at the shortest focal length, F_(s),namely 35.01 mm, the length from the vertex of the front surface R₄₁ ofthe front element A" of the film plane 23", is 58.94 mm and thetelephoto ratio, i.e. the ratio of that length, 58.94 mm, to the focallength, F_(s), is 1.68 which is less than 1.8. Also, at the long focallength F_(L), of 104.88 mm, the length from the front surface R₄ of thefront element A" to the film plane 23" is 93.80 mm which is less thanthe focal length F_(L).

The clear aperture of the lens A" is 22.75 mm which, together with theshortness of the distance between the vertex of the front surface R₄₁ ofthe front lens A" and the film plane 23", ensures that a separateviewfinder can be placed close to the lens without intruding on thefield of view of the viewfinder, thus minimizing viewfinder parallax.

The values of L=F/F_(s) were given above for each of the components ofeach of the three embodiments and they were:

    __________________________________________________________________________            Embodiment 1                                                                              Embodiment 2                                                                              Embodiment 3                                  COMPONENT                                                                             L   +10%                                                                              -10%                                                                              L   10% -10%                                                                              L   +10%                                                                              -10%                                  __________________________________________________________________________    27      -1.41                                                                             -1.55                                                                             -1.56                                                                             -1.56                                                                             -1.72                                                                             -1.40                                                                             -1.69                                                                             -1.86                                                                             -1.52                                 29      0.79                                                                              0.87                                                                              0.71                                                                              0.77                                                                              0.85                                                                              0.69                                                                              0.79                                                                              0.87                                                                              0.71                                  31      1.58                                                                              1.74                                                                              1.42                                                                              1.29                                                                              1.42                                                                              1.16                                                                              1.37                                                                              1.51                                                                              1.23                                  33      -0.72                                                                             -0.79                                                                             -0.71                                                                             -0.55                                                                             -0.61                                                                             -0.50                                                                             -0.57                                                                             -0.63                                                                             -0.51                                 __________________________________________________________________________

In the table immediately above ±10% values are given for each of the Lvalues. It will be seen that the largest and smallest L values in thetable for each of the components are:

    ______________________________________                                                       Largest  Smallest                                              Component      L        L                                                     ______________________________________                                        27             -1.86    -1.27                                                 29             0.87     0.69                                                  31             1.74     1.16                                                  33             -0.79    -0.50                                                 ______________________________________                                    

Embodiments of the present invention may be successfully constructedwith the following ranges:

-1.86Fs<F₁ <-1.27Fs

0.87Fs>F₂ >0.69Fs

1.74Fs>F₃ >1.16Fs

-0.79Fs<F₄ <-0.50Fs

wherein F₁, F₂, F₃ and F₄ are the focal lengths of the components 27,29, 31 and 33, respectively.

While in the above-described three embodiments the zoom ratios are2.98:1; 2.99:1; and 3.00:1, respectively, it is believed that theinvention may be embodied successfully in zoom lenses having a ratioclose to 2.5:1.

The invention has been described in detail with particular reference topresently preferred embodiments, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. A zoom lens comprising four components eachmovable axially to vary the focal length through a range of at least2.5:1, including a front negative component, a positive component, apositive cemented doublet component and a rear negative componentcomprising three elements, and a diaphragm mounted with thefirst-mentioned positive component, the total length from the vertex ofthe front surface of the front lens element to the focal plane beingless than 1.8F_(s) at the short focal length setting and less than F_(L)the long focal length setting, wherein F_(s) is the short focal lengthand F_(L) is the long focal length.
 2. A zoom lens as claimed in claim1, wherein with the ratios VR of the Abbe V numbers of the elements ofsaid positive cemented doublet greater than unity 3>VR>1.8.
 3. A zoomlens as claimed in claim 1 or 2, wherein said negative componentcomprises front, second, and rear elements and with the ratio VR₁₂ ofthe Abbe V numbers of the front and second element greater than unity3>VR₁₂ >1.3.
 4. A zoom lens as claimed in claim 1, wherein the positivecemented doublet component includes a front element having a refractiveindex N_(C) and a rear element having a refractive index N_(D) andwherein 0.4>|N_(C) -N_(D) |>0.1.
 5. A zoom lens as claimed in claim 4,wherein with the ratio VR of the Abbe V numbers of the elements of saidpositive cemented doublet greater than unity 3>VR>1.8 and said negativecomponent includes front, second and rear elements and with the ratioVR₁₂ of the Abbe V numbers of the front and second elements greater thanunity 3>VR₁₂ >1.3.
 6. A zoom lens assembly made substantially accordingto the following specifications:

    __________________________________________________________________________                                           REFRACTIVE                                                                             Abbe                                                                 INDEX    No.                           GROUP                                                                              LENS                                                                              RADIUS   THICKNESS                                                                             SPACING      N.sub.d  V.sub.d                       __________________________________________________________________________                              S.sub.1 = ∞                                            R.sub.1 = -25.7439                                                   27   A            t.sub.1 = 2.500      1.71301  53.8                                   R.sub.2 = -99.0606                                                                                  7.622 at 35.06                                                                5.789 at 50.48                                                           S.sub.2 =                                                                          3.266 at 72.77                                                                1.000 at 104.56                                         Diaphragm                                                                                      FS.sub.1 = 0.200                                             R.sub.3 = asphere                                                    29   B            t.sub.3 = 3.800      1.80400  46.6                                   R.sub.4 = -50.2153                                                                                  8.023 at 35.06                                                                7.420 at 50.48                                                            S.sub.3 =                                                                         6.221 at 72.77                                                                5.109 at 104.56                                         R.sub.5 = 46.3678                                                         C            t.sub.4 = 1.500      1.84666  23.8                          31       R.sub.6 = 16.5287                                                         D            t.sub.5 = 6.269      1.49783  67.0                                   R.sub.7 = -23.9031                                                                                  8.699 at 35.06                                                                4.353 at 50.48                                                           S.sub.4 =                                                                          1.972 at 72.77                                                                0.500 at 104.56                                         R.sub.8 = -50.4295                                                        E            t.sub.7 = 4.58       1.84666  23.8                                   R.sub.9 = -18.7258                                                                             FS.sub.2 = 0.100                                             R.sub.10 = -22.1134                                                  33   F            t.sub.9 = 1.8        1.79952  42.2                                   R.sub.11 = -58.7660                                                                            FS.sub.3 = 3.588                                             R.sub.12 = -16.8917                                                       G            t.sub.11 = 2.00      1.69100  54.7                                   R.sub.13 = 146.044                                                                                  8.25 at 35.06                                                                 21.80 at 50.48                                                           S.sub.5 =                                                                          39.76 at 72.77                                                                64.20 at 104.56                                __________________________________________________________________________


7. A zoom lens assembly made substantially according to the followingspecifications:

    __________________________________________________________________________                                            REFRACTIVE                                                                             Abbe                                                                 INDEX    No.                          GROUP                                                                              LENS                                                                              RADIUS   THICKNESS                                                                             SPACING       N.sub.d  V.sub.d                      __________________________________________________________________________                              S.sub.1 ' = ∞                                          R.sub.21 = -26.5947                                                  27'  A'           t.sub.21 = 2.500      1.57958  53.7                                  R.sub.22 = -166.152                                                                                  7.771 at 35.02                                                                7.353 at 50.49                                                          S.sub.2 ' =                                                                         4.816 at 72.80                                                                1.000 at 104.79                                        Baffle                                                                                         FS.sub.21 = 0.200                                            R.sub.23 = asphere                                                   29'  B'           t.sub.22 = 4.000      1.53172  48.8                                  R.sub.24 = -27.4940                                                                            FS.sub.22 = 4.600                                            Diaphragm                                                                                            4.419 at 35.02                                                                3.312 at 50.49                                                          S.sub.3 ' =                                                                         2.183 at 72.80                                                                1.563 at 104.79                                        R.sub.25 = 54.4437                                                        C'           t.sub.23 = 1.5        1.84666  23.8                                  R.sub.26 = 15.0805                                                   31'  D'           t.sub.24 = 5.125      1.49783  67.0                                  R.sub.27 = -17.0839                                                                                  6.161 at 35.02                                                                2.723 at 50.49                                                          S.sub.4 ' =                                                                         1.121 at 72.80                                                                0.500 at 104.79                                        R.sub.28 = -40.7438                                                       E'           t.sub.25 = 5.645      1.84666  23.8                                  R.sub.29 = -10.5410                                                  33'  F'           t.sub.26 = 3.890      1.70181  41.0                                  R.sub.30 = -150.263                                                                            FS.sub.23 = 3.890                                            R.sub.31 = -13.9956                                                       G'           t.sub.27 = 2.000      1.65016  39.2                                  R.sub.32 = 1438.91                                                                                   7.95 at 35.02                                                                 21.46 at 50.49                                                          S.sub.5 ' =                                                                         38.41 at 72.80                                                                58.69 at 104.79                               __________________________________________________________________________


8. A zoom lens assembly made substantially according to the followingspecifications:

    __________________________________________________________________________                                            REFRACTIVE                                                                             Abbe                                                                 INDEX    No.                          GROUP                                                                              LENS                                                                              RADIUS   THICKNESS                                                                             SPACING       N.sub.d  V.sub.d                      __________________________________________________________________________                              S.sub.1 " = ∞                                          R.sub.41 = -28.9346                                                  27"  A"           t.sub.41 = 2.5        1.58913  61.3                                  R.sub.42 = -170.955                                                                                  8.701 at 35.01                                                                8.040 at 50.48                                                          S.sub.2 " =                                                                         4.990 at 72.79                                                                0.800 at 104.88                                        R.sub.43 = ashpere                                                        .sup. B.sub.a "                                                                            t.sub.42 = 1.500      1.59044  30.9                                  R.sub.44 = 32.5160                                                   29"                       FS.sub.31 = 0.200                                            R.sub.45 = 26.4507                                                        .sup. B.sub.b "                                                                            t.sub.43 = 4.400      1.54072  47.2                                  R.sub.46 = -32.5160                                                                            FS.sub.32 = 3.500                                            Diaphragm                                                                                            3.759 at 35.01                                                                2.433 at 50.48                                                          S.sub.3 " =                                                                         1.226 at 72.79                                                                0.612 at 104.88                                        R.sub.47 = 45.5291                                                        C"           t.sub.44 = 1.500      1.84666  23.8                         31"      R.sub.48 = 14.1057                                                        D"           t.sub.45 = 5.234      1.49783  67.0                                  R.sub.50 = -18.6600                                                                                  6.187 at 35.01                                                                2.786 at 50.48                                                          S.sub.4 " =                                                                         1.204 at 72.79                                                                0.500 at 104.88                                        R.sub.51 = -49.1546                                                       E"           t.sub.46 = 5.330      1.84666  23.8                                  R.sub.52 = -10.7888                                                  33"  F"           t.sub.47 = 1.800      1.70181  41.0                                  R.sub.54 = -220.343                                                                            FS.sub.33 = 3.540                                            R.sub.55 = -14.5565                                                       G"           t.sub.48 = 2.000      1.65016  39.2                                  R.sub.56 = 201.766                                                                                   8.79 at 35.01                                                                 22.61 at 50.48                                                          S.sub.5 " =                                                                         39.69 at 72.79                                                                60.38 at 104.88                               __________________________________________________________________________


9. A zoom lens comprising four components each movable axially to varythe focal length through a range of at least 2.5:1, including a frontnegative component having a focal length F₁, a positive component havinga focal length F₂, a positive cemented doublet component having a focallength F₃ and a negative component comprising three elements having afocal length F₄, the shortest focal length being F_(s),wherein:-1.86F_(s) <F₁ <-1.27F_(s) 0.87F_(s) >F₂ >0.69F_(s) 1.74F_(s)>F₃ >1.16F_(s) -0.79F_(s) <F₄ <-0.50F_(s).
 10. A zoom lens comprisingfour components each movable axially to vary the focal length through arange of at least 2.5:1, including a front negative component having afocal length F₁, a positive component having a focal length F₂, apositive cemented doublet component having a focal length F₃ and anegative component comprising three elements having a focal length F₄,the shortest focal length being F_(s), wherein:-1.55F_(s) <F₁<-1.27F_(s) 0.87F_(s) >F₂ >0.17F_(s) 1.74F_(s) >F₃ >1.42F_(s) -0.79F_(s)<F₄ <-0.71F_(s).
 11. A zoom lens comprising four components each movableaxially to vary the focal length through a range of at least 2.5:1,including a front negative component having a focal length F₁, apositive component having a focal length F₂, a positive cemented doubletcomponent having a focal length F₃ and a negative component comprisingthree elements having a focal length F₄, the shortest focal length beingF_(s), wherein: -1. 72F_(s) <F₁ <-1.40F_(s) 0.85F_(s) >F₂ >0.69F_(s)1.29F_(s) >F₃ >1.16F_(s) -0.61F_(s) <F₄ <-0.50F_(s).
 12. A zoom lenscomprising four components each movable axially to vary the focal lengththrough a range of at least 2.5:1, including a front negative componenthaving a focal length F₁, a positive component having a focal length F₂,a positive cemented doublet component having a focal length F₃ and anegative component comprising three elements having a focal length F₄,the shortest focal length being F_(s), wherein:-1.86F_(s) <F₁<-1.52F_(s) 0.87F_(s) >F₂ >0.71F_(s) 1.51F_(s) >F₃ >1.23F_(s) -0.63F_(s)<F₄ <-0.51F_(s).